example mysql query to update a table

Can anyone come up with a query to do this:

Table1 contains uk postcodes (the key field), counties and towns - approx 2m recs - in the following formats:
AB11 2AB, B23 1AD, B1 3AR, etc.

Table2 is a much smaller one containing the same data except that the postcode/key field only has the first part of the postcode - before the space.

I need to update all records in Table1 with the town and county data from Table2, where the part of the key, before the space, equals the key of Table2